Search

Copyright of Iron Steel Vanadium Titanium is the property of Iron Steel Vanadium Titanium Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Vacuum arc remelting is the main production method of titanium alloy ingots at present. In order to obtain good quality ingots, it is of great significance to study the formation of the solidification structure of ingots via vacuum arc remelting. In order to select and optimize the nucleation parameters for the solidification microstructure simulation of an ingot, a 3D CAFE model for microstructure evolution during vacuum arc remelting was established, taking into account heat transfer, flow, and solute diffusion. The Gaussian distribution continuous nucleation model and extended KGT model were used to describe the grain nucleation and dendrite tip growth rates, respectively. The multi-point mass source and moving boundary method were used to simulate the ingot growth. The results show that there are three typical crystal regions in the solidification structure of vacuum arc remelting titanium alloy ingots, namely the surface fine crystal region, columnar crystal region, and central equiaxed crystal region. The proportion of the columnar crystal region in the solidification structure of an ingot increases gradually with the increase in the undercooling of the maximum bulk nucleation. With an increase in the maximum bulk nucleation density, the equiaxed grain zone gradually increases, and the grain size gradually decreases. The proportion of the columnar crystal region in the solidification structure of an ingot increases gradually with an increase in the undercooling of the maximum bulk nucleation. The maximum volume nucleation variance has no obvious effect on the change in the solidification structure. When the maximum volume nucleation undercooling is 5.5 K, the maximum volume nucleation standard deviation is 4 K, and the maximum volume nucleation density is 5 × 108. The solidification structure simulation results are in good agreement with the experimental results. [ABSTRACT FROM AUTHOR]

In this study, the morphology characteristics and formation mechanism of channel segregation in the industrial-sized Ti–Nb binary ingots produced by vacuum arc remelting (VAR) are researched based on experiments and calculations. The results show that the channel segregation is usually located at the 1/4–3/4 radius of the ingot and the morphology is closely related to the VAR process. The Ti-enriched channel segregation stripes tend to parallel to the ingot centerline and columnar dendrites in steady-state remelting region and hot-top region, respectively, while along the molten pool profile in residual molten pool region. For the first time, the Ti2O3 particles precipitated in the channel segregation were observed, following the orientation relationship of β//Ti2O3 and {11‾0}β//{011‾}Ti2O3 with β matrix in coherent boundary. First-principles calculations evident that the enrichment of Ti-solute tends to decrease the formation enthalpy, and hence makes for the precipitation of Ti2O3 particles. The numerical simulation and the experiment results manifest that the channel segregation originates from the convergence of interdendritic Ti-enriched liquid, resulting in the density inversion between the Ti-enriched initiation site and the surrounding liquid. The density gradient and the solidification rate dominate the growth direction and the radius distribution of the channel segregation. Based on the above, an optimized technique with helium cooling and the external stirring magnetic field was conducted and the channel segregation was eliminated successfully.

Copyright of Iron Steel Vanadium Titanium is the property of Iron Steel Vanadium Titanium Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In order to study the influence of the vacuum arc remelting process (VAR) on the grain structure of the ingot and provide initial condition for the prediction and analysis of the subsequent process such as homogenization and billet forging, an efficient and accurate three-dimensional (3D) cellular automata method was developed for the VAR process, and all parts of the algorithm were rigorously verified, and it can be combined with the MeltFlow-VAR. An ingot of 718 alloy was smelted through experiment for calculation verification and proved the accuracy of the predictions. A new method for discretization of Euler angles to obtain orientation index is proposed and verified, which is more flexible and higher computationally efficient than previous algorithms. Aiming at the problem of a large number of cells and calculation time on large-scale VAR ingot in the future, a hybrid parallel scheme is designed, and it is expected to realize large-scale calculations on the supercomputer system. Finally, the effect of different cell sizes on the calculation results was also studied, and the grain size at the edge of the ingot was not affected by the cell size.

Numerical modeling and industrial experiment were used to study the entire vacuum arc remelting (VAR) process of 660 mm GH4742 superalloy. In order to calculate the electromagnetic field, flow field, temperature field, and melt pool shape change throughout the entire VAR process, a 2D axisymmetric model with coupled multi-physical fields matching industry trials was constructed. The microstructure and elemental distribution conditions in the large-size GH4742 ingot were analyzed in combination with the industrial ingot dissection experiment, and the most likely locations of freckle defects were predicted. According to the research, the melt pool has two clockwise flow fields that are affected by buoyancy and Lorentz forces. The melt pool depth deepens gradually as melting proceeds, with a maximum melt pool depth of 0.32 m and a paste zone width of 0.16 m. Although the ingot's elemental distribution is largely consistent, there is microsegregation between the dendrites. Where the freckle is most likely to appear, at (0.322, 0.075), the Rayleigh has a great value of 1.1. For melt pool form and dendritic spacing throughout the entire melting process, the results of the industrial ingot dissection experiment and the simulation results show good agreement, proving the accuracy of the thermal history and solidification microstructure calculation for the entire melting process. Furthermore, the prospect of combining numerical simulation with a special material database for accurate defect prediction is proposed.

Titanium alloy (Ti6Al4V) is extensively used in the fabrication of upper stage propellant tanks for satellite launch vehicles. These tanks are of welded construction and are made from three types of domes and 5 types of rings. This paper investigates the occurrence of X-ray radiography and fluorescent penetrant indications in a specific ring component of the tank assembly after machining to thickness of 1.7 mm. The affected ring, with dimensions OD-φ1400 mm, ID-φ1300 mm, and height 410 mm, exhibited a multitude of surface and embedded indications across eight sectors, spanning approximately 140 mm in height at the mid-section of the ring. To ascertain the root cause of these indications, a comprehensive metallurgical analysis was conducted, involving X-ray radiography, optical/electron microscopy, and mechanical testing. By correlating non-destructive observations with microscopic findings, this study establishes that the occurrence of defects can be attributed to a combination of raw material and deformation processing issues. The results contribute to a better understanding of the factors influencing the quality of Ti6Al4V propellant tank rings and aid in the development of improved manufacturing processes. [ABSTRACT FROM AUTHOR]

Abstract—When vacuum arc remelting (VAR) of a Ti–10V–2Fe–3Al alloy is performed, automatic control of the electrode gap in a given average voltage range is shown to be impossible. The voltage signal is found to have reversed polarity pulses. The duration of such pulses is distributed according to the Weibull statistics. Based on this finding, we are the first to design a regulator for automatic control of the electrode gap for melting Ti–10V–2Fe–3Al alloy ingots. [ABSTRACT FROM AUTHOR]

The electromagnetic stirring force generated by the axial magnetic field (AMF) interacting with the process current greatly affects the solidification process and consequently the metallurgical quality of ingots, but there are few studies about the effect of AMF on the multi-physics field involving solute transport during VAR process. Based on this, a three-dimensional full-size transient model has been developed to investigate the role of AMF on the metallurgical quality evaluated by the segregation defect and solidification quality in this paper. All essential considerations of the fluid flow, heat transfer and solute transport are incorporated in the model. Both the local solidification time (LST) and secondary dendrite arm spacing (SDAS) are adopted as indexes to characterize the solidification quality. The results show that the stirring force caused by the AMF greatly promotes the downward heat transfer and thus leads to deeper molten pool. The final value of volume-averaged segregation extent is greatly reduced by 24.13% as the AMF intensity increases from 0 to 50 G, while the difference of this value between 50 G and 100 G is only 1.96%. The volume-averaged values of the LST and SDAS are all reduced with the increase of AMF intensity, in which both values change from 1088 s to 190 μm without AMF to 890 s and 182 μm under 100 G. These results indicate that the application of AMF can significantly improve the metallurgical quality of ingots, but this effect becomes more and more limited with the increase of AMF intensity.

The different heat transfer conditions in each region of the vacuum arc remelting superalloy ingot lead to significant difference in the morphology and size distribution of carbide in the ingot. Based on industrial vacuum arc remelting GH4742 alloy as a raw material, using metallographic and scanning electron microscopic analysis quantitative analysis method to study the ingot different position distribution of the carbide precipitation behavior and microstructure, supplemented by MeltFlow-VAR simulation software, the solidification process of remelting different cooling rate and local solidification time on the influence of carbide were analyzed. The results show that Nb and Ti elements are enriched in the carbide precipitates of GH4742 alloy, and the segregation degree of Nb element is the largest. The area of the precipitated phase is decreased from the center to the edge, and the morphology is changed from skeleton-like and cursive to interconnected fine strips. As the cooling rate increases, the dendrites become more slender and compact, and the dendrite spacing decreases. The area of precipitated phase is linearly related to the secondary dendrite spacing. Increasing the cooling rate can reduce the dendrite spacing, thus the area of precipitated phase is reduced effectively.

The arc characteristics especially the arc distribution of the vacuum arc remelting (VAR) process are closely related to the ingot evolution and consequently the final product quality. Taking segregation defects and solidification quality as the indexes to evaluate the final product quality under different arc distributions, a three-dimensional full-scale transient model for predicting segregation defects is developed in this paper. Local solidification time (LST) and secondary dendrite arm spacing (SDAS) are used to characterize the solidification quality. This model is adopted to predict channel segregation (freckle) and macrosegregation defects during VAR process of Ni-5.8 wt.%Al-15.2 wt.%Ta alloy under several typical arc distributions. The results show that the diffuse arc has the shallowest molten pool among several arc distributions. At the early stage of solidification, the solute enrichment channels formed under the Gaussian and diffuse arc are slender and concentrated, while they are relatively sparse and uneven in thickness under the rotating arc. The value of volume-averaged segregation extent is always the smallest under the diffuse arc and the largest under the Gaussian arc, with final values of 67.53% and 69.66%, respectively. The volume-averaged values of LST and SDAS are relatively the largest under the Gaussian arc, about 1599 s and 209 μm, respectively; and they are the smallest under the diffuse arc, about 1520 s and 206 μm, respectively. In the same process conditions, the product quality of VAR ingots prepared under the diffuse arc is the best, followed by the rotating arc, and the worst under the Gaussian arc.

Copyright of Journal of Aeronautical Materials is the property of Editorial Board of Journal of Aeronautical Materials and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The following main types of segregation defects inherent in many titanium-based alloys are considered: zonal segregation (macrosegregation), tree-like structure (tree-like segregation), and β-flecks. The possible mechanisms of their formation are discussed. The influence of chemical composition on the melting and beta transus temperatures is considered. [ABSTRACT FROM AUTHOR]

Current intensity is a critical parameter in the vacuum arc remelting (VAR) process, significantly impacting the molten pool, solidification structure, and ultimately, the quality of the ingot. This study establishes a transient electromagnetic-fluid-thermal-solidified coupled model to examine the effects of current intensity on the shape of molten pool and the solidification process of Ti60 alloy ingots produced by VAR process. Findings indicate that with the increase in current intensity, there is a corresponding rise in the magnetic induction intensity, current density, and Lorentz force. This enhancement leads to more vigorous flow in the liquid phase, creating a vortex flow opposing to the ingot's center at the boundary, influenced by the strong current. As a consequence, the molten pool's shape tends to shift from a “V” shape to a “U” shape, and the depth of molten pool increases while the mushy zone thickness diminishes. For instance, at 17000 A, the depth of molten pool surges by 57.43%, and the mushy zone thickness contracts by 62.01% compared to 5000 A. Over time, the depth of molten pool gradually decreases, with its reduction range (Δh) within 400 to 6000 s inversely related to current intensity. At 17000 A, Δh is 23.71% less than at 5000 A. Furthermore, elevating the current intensity results in a higher temperature gradient within the ingot and a marked reduction in local solidification time, particularly in the ingot's central area. [ABSTRACT FROM AUTHOR]

Vacuum Arc Remelting is an important method of processing reactive and refractory liquid metal alloys, including titanium and zirconium alloys. Recent measurements of the electric arc dynamics under the presence of a time-varying magnetic field during an industrial melt of a Ti64 alloy provided evidence of the existence of an ensemble arc motion. Such motion is responsible for transient and non-axisymmetric inputs of electric current and energy at the top surface of the remelted ingot. The present work is an attempt to evaluate, using a simplified numerical simulation approach, to what extent the solidification conditions of the VAR ingot and, consequently, the quality of the final product, may be affected by this phenomenon. The reported results indicate that, under the worst case conditions, the relative vanadium segregation in the solidified ingot can reach values as high as 12.5%. [ABSTRACT FROM AUTHOR]

The results of studying the possibility of obtaining ingots from zirconium alloy of Zr‒Nb‒Ti system, using the method of vacuum arc remelting with a consumable electrode, are presented. Ingots of 50 mm diameter produced by remelting with a non-consumable electrode in a skull furnace were used as consumable electrodes. The technology of producing a zirconium alloy of a given composition by the method of vacuum-arc remelting of a consumable electrode into a copper mould has been developed. A complex of technological and material science problems was solved, a study of technological factors, metallurgical methods and processes, associated with selection of melting equipment and fixtures was carried out, a technological process was developed for obtaining ingots of a given homogeneous chemical composition for further deformation processing and producing an initial billet. An ingot of 120 mm diameter was melted in a vacuum arc furnace. The technological parameters of melting during arc remelting with a consumable electrode in a vacuum arc furnace were determined. A study of ingot metal of an experimental alloy of Zr‒Nb‒Ti system by the method of ultrasonic flaw detection showed absence of internal structural defects, namely discontinuities, shrinkage cavities, porosity or large non-metallic inclusions. Ref. 16, Table. 2, Fig. 3. [ABSTRACT FROM AUTHOR]

In this paper, the finite element and cellular automaton coupling (CAFE) model is used to simulate the solidification process of a large ingot during vacuum consumable arc melting (VAR). The effects of melting temperature, melting rate, and mold cooling coefficient on temperature field distribution and solidification structure were studied by simulation. The results show that the microstructure predicted by the numerical method is consistent with the experimental results. As the melting temperature increases from 1500 °C to 1800 °C, the depth of the molten pool increases from 14 mm to 24 mm, the width of the mushy zone decreases from 10 mm to 9 mm, and the average radius of the grains increases from 584.3 μ m to 679 μ m. With the increase in melting rate from 6 kg min ^−1 to 12 kg min ^−1 , the maximum depth of the molten pool increases from 4 mm to 32 mm, the width of the mushy zone increases from 8 mm to 13 mm, and the average grain radius decreases from 943 μ m to 497 μ m. As the cooling coefficient of the mold increases from 1000 W m ^−2 ·K ^−1 to 5000 W m ^−2 ·K ^−1 , the depth of the molten pool decreases from 16.7 mm to 12 mm, the width of the mushy zone decreases from 7.3 mm to 5.9 mm, and the average radius of the grains increases from 630 μ m to 1303.5 μ m.

Vacuum Arc Remelting is an important method of processing reactive and refractory liquid metal alloys, including titanium and zirconium alloys. Recent measurements of the electric arc dynamics under the presence of a time-varying magnetic field during an industrial melt of a Ti64 alloy provided evidence of the existence of an ensemble arc motion. Such motion is responsible for transient and non-axisymmetric inputs of electric current and energy at the top surface of the remelted ingot. The present work is an attempt to evaluate, using a simplified numerical simulation approach, to what extent the solidification conditions of the VAR ingot and, consequently, the quality of the final product, may be affected by this phenomenon. The reported results indicate that, under the worst case conditions, the relative vanadium segregation in the solidified ingot can reach values as high as 12.5%.

Segregation defects greatly affect the service performance and working life of castings during the vacuum arc remelting (VAR) process. However, the corresponding research on the prediction of segregation defects is still not comprehensive. Through considering the influence of water-cooled crucible on the electromagnetic field inside an ingot, a full-scale model for the comprehensive prediction of freckles and macrosegregation defects during the VAR process is developed in this paper. The macroscopic solute transport phenomenon and the segregation behavior of Ni-5.8 wt% Al-15.2 wt% Ta alloy are predicted. The results indicate that the freckles are mainly concentrated in the lower region of the ingot. With the growth of the ingot, the solute enrichment channels gradually develop into solute enrichment regions, and the channel segregation evolves into macrosegregation. The Lorentz force mainly affects the flow pattern at the top of the molten pool, while the complex flow of multiple vortices is dominated by thermosolutal buoyancy. The maximum and minimum relative segregation ratio inside the ingot can reach 290% and −90%, respectively, and the positive segregation region accounts for about 79% of the total volume. This paper provides a new perspective for understanding the segregation behavior inside the ingot by studying the segregation evolution during the VAR process.

This study investigates the microstructures and the mechanical properties of equiatomic Ti20Mo20Ta20Nb20V20 and nonequiatomic Ti40Mo15Ta15Nb15V15 and Ti60Mo10Ta10Nb10V10 HEAs using X-ray diffraction (XRD) analysis, field emission scanning electron microscope (FE-SEM), and micro-Vickers hardness test. The specimens were fabricated using the vacuum arc remelting (VAR) process and homogenized at a temperature of 1300°C for 4 h in a vacuum atmosphere. The determined thermodynamic parameters, Ω ≥ 1.1, δ ≤ 6.6%, and VEC < 6.87, suggested that the HEAs consisted of BCC solid solutions. XRD patterns of all the HEAs displayed single BCC phases. The difference in the solidification rate led to the micro-segregation associated with the elements Ta and Mo enriched in the dendrite arms and the elements V and Ti in the inter-dendritic regions. The HEA specimens showed a decrease in hardness with higher concentration of Ti element because the intrinsic hardness of Ti is lower as compared to the intrinsic hardness of Nb and Mo. [ABSTRACT FROM AUTHOR]

Copyright of Rare Metal Materials & Engineering is the property of Northwest Institute for Nonferrous Metal Research and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Rare Metal Materials & Engineering is the property of Northwest Institute for Nonferrous Metal Research and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This research aims to prepare high quality powder of Ti-6.5Al-1.4Si-2Zr-0.5Mo-2Sn,which lays foundation for the following preparation of powder high temperature titanium alloy component.Ti-6.5Al-1.4Si-2Zr-0.5Mo-2Sn alloy ingots were prepared by vacuum arc remelting (VAR). The chemical compositions of ingots were examined. The loss of alloy elements, uniformity of composition, phase composition and microstructure of titanium alloy ingots were analyzed. Then powders were prepared by plasma rotating electrode process (PREP) with different rotating speeds. Alloy powders were sieved into different particle sizes. The relationship between rotating speed and physical and chemical properties of powder was studied. X-ray diffraction(XRD), scanning electron microscope(SEM) and metallurgical microscope(OM) were used to investigate the phase composition, morphology and microstructure of the powder. The results show that the composition distribution of titanium alloy ingot prepared by VAR is uniform and the content of alloy elements meets the requirements of national standard, through a unique pressing electrode. Microstructure of the ingot is lamellar structure with small amounts of silicide particles disperse in the matrix. The size distribution of the powders made by PREP method exhibits the normal distribution. The sphericity of the powder is excellent,and no hollow ball and satellite ball exists. With the increase of rotating speed, the proportion of small particles increases dramatically,the proportion of large particles decreases greatly. The phase composition of powder is mainly α' phase,and it is mainly composed of peritectic and small amount of dendrite structures. Compared with the alloy ingot, the elements of the powders have a slight loss, the content of O is less than 0.1%,which is beneficial to obtain high-performance powder titanium alloy.

Abstract Understanding the arc dynamics during VAR is important for controlling the final quality of the ingot, as the spatial and temporal distribution of the arc dictates the electric current and energy inputs at the ingot top, which in turn affect the hydrodynamics of the metal in the molten pool and the solidification conditions of the ingot. The arc dynamics during vacuum arc remelting was quantitatively investigated based on the analysis of the light emitted by the arc and reflected by the molten pool using photodiodes placed inside a full-scale furnace. The measurements allowed us to determine the location of the arc luminosity centroid and to follow its displacement as a function of time. They were made during the melt of a Ti64 alloy with an imposed alternated electromagnetic stirring of high intensity. The arc dynamics was found to be most of the time periodic, asymmetrical, and strongly correlated to the evolution of the stirring magnetic field. The arc centroid exhibited three regular displacement patterns throughout the melt. A common characteristic to all three patterns was the relative stability of the centroid during stirring plateaus and its rapid motion during stirring ramps. An evolution towards a much more centered distribution of the centroid was observed with the arc power decrease during the hot-topping phase. Possible implications of the observed arc dynamics on the final quality of the VAR ingot are discussed. [ABSTRACT FROM AUTHOR]

Copyright of Electrometallurgy Today / Sovremennaya Elektrometallurgiya is the property of International Association Welding (Paton Publishing House) and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Abstract: A thermal model is developed for the ingot solidification during vacuum arc remelting (VAR) and is applied to calculate pool profiles for a VT3-1 alloy. The pool profiles are calculated for two remelting schedules, and the calculation results are compared with radiography data. The model calculation results are shown to agree satisfactorily with experimental data. The model is used in practice to develop conditions for the final remelting of a VT3-1 alloy to exclude the formation of segregation defects, namely, β flakes and macrosegregation. The developed model can be used for technological calculations and can give important information on the dynamics of VAR ingot solidification. [ABSTRACT FROM AUTHOR]

Nb-Ti alloys are normally produced by vacuum arc remelting process. Due to inadequate processing parameters, freckles can be observed in macroetched ingots. In the present work, visual, chemical, metallographic, and X-ray are presented which establish the appearance, composition, microstructure differences between freckle regions and normal regions. It has been observed that in freckles parallel to the ingot axis, the Ti content is up to 53wt%, 7wt% higher than normal regions. It is also shown that a lot of precipitation phases appeared in freckle regions, because of the thermosolutal convection in the mushy zone. The Rayleigh number, which recommended as a criterion for freckle initiation, has been calculated that using a VAR melting software. Based on the experimental results and simulation results, it is concluded that freckles can be influenced by processing parameters, and freckles in Nb-Ti alloy can be eliminated by matching appropriate processing parameters.

The determination of an appropriate amount of turning for superalloy ingot surfaces, in a scientific and reasonable manner, is vital to the improvement of the metallurgical quality and comprehensive performance of superalloy ingots. In the present study, scanning electron microscopy with energy-dispersive spectroscopy, a high-temperature testing machine, a Brinell hardness tester and the Image-Pro Plus software were used to analyze and compare the types and amounts of inclusions, the average area of the (Al,Mg)O inclusions, and the mechanical properties of points at different distances from the edge of the GH4169 superalloy vacuum arc remelting (VAR) ingot edge. The effects of the amount of turning to which the superalloy is subjected, the metallurgical qualities, and the mechanical properties were systematically studied. The results showed that the five inclusion types did not change as the sampling locations moved away from the ingot edge, but the amount of inclusions and the average area of the (Al,Mg)O inclusions first decreased and then stabilized. Similarly, the tensile strength, elongation, section shrinkage, hardness, and fatigue life first increased and then stabilized. Finally, this experiment tentatively determined that an appropriate amount of turning for a GH4169 superalloy ingot is 36−48 mm.

The columnar-to-equiaxed transition in the solidification of a Ti-10V-2Fe-3Al alloy is considered during vacuum arc remelting. A GV curve is plotted using a linear model of a multicomponent alloy along with modified Hunt (to determine temperature gradient G as a function of supercooling Δ T) and Ivantsov (to determine the concentrations at the dendrite tip versus liquidus isotherm velocity V) models. The unknown parameters of the models are determined by comparing the results of model calculations with experimental data, which are also obtained in this work. The plotted GV curve is compared with the GV curve of a VT3-1 alloy. [ABSTRACT FROM AUTHOR]

Statistical analysis of the chemical composition of high-temperature VZh159 nickel alloy in vacuum-induction melting and vacuum arc remelting yields regression equations that may be used to predict the metal composition in the ingots obtained by vacuum arc remelting as a function of the components in the consumable electrodes. The variation in oxygen, carbon, nitrogen, sulfur, and phosphorus concentrations in remelting is determined. The results are used in the design of production processes for high-temperature nickel-alloy ingots at PAO Ruspolimet. [ABSTRACT FROM AUTHOR]

Copyright of BHM Berg- und Hüttenmännische Monatshefte is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Vacuum arc remelting (VAR) is an ultra-high temperature and opaque process. It is difficult to conduct experimental research on the melt flow behavior and the formation of macrosegregation in this process. This work develops a two-dimensional Eulerian three-phase model to predict the solidification structure and macrosegregation of industrial Ti 2 AlNb ingots under complex multi-physics mechanism. The model is also used to study the influence of stirring magnetic field on the melt flow behaviors and macrosegregation of VAR ingots. The results show that Al content of the columnar zone increases gradually from the outside to the inside due to the flow behavior of the melt and the sedimentation of equiaxed grains. External magnetic field applied to stabilize the arc also makes significant effects on the melt convection and macrosegregation. Stirring Lorentz force induced by the external magnetic field drives the melt flow to rotate as a centrifugal force in the top, while drives the melt to flow downward along the metal pool and reduces the influence of the self-induced Lorentz force in the bottom. Superimposing the proper stirring magnetic field on the self-induced magnetic field can strengthen the solute mixing in the molten pool and improve the overall macrosegregation degree of the ingot. Increasing the stirring magnetic field can improve negative segregation in the center of the ingot but intensify the positive segregation in the periphery of the ingot. [ABSTRACT FROM AUTHOR]

The effect of combined addition of carbon and titanium on structure and properties of Fe-7 wt%Al alloys has been studied. Pancakes of four alloys with nominal compositions, Fe-7Al-0.05C-0.2Ti (alloy-1), Fe-7Al-0.5C-2.0Ti (alloy-2), Fe-7Al-1.0C-4.0Ti (alloy-3) and Fe-7Al-2.0C-8.0Ti (alloy-4) were prepared by non-consumable arc melting. The arc melted pancakes were examined using scanning electron microscopy, electron probe microanalysis, and X-ray diffraction to understand the microstructure of these alloys. The dendritic solidification structure was observed in alloys 2-4. The microstructure of these alloys also revealed the presence of TiC precipitates, whereas no such phase was observed in alloy 1. The size and volume fraction of these precipitates increased with increase in the concentration of Ti and C. The yield strength of Fe-7 wt%Al alloy at both room temperature and at 873 K increases with increasing carbon and titanium.This may be due to the composite strengthening arising out of increased precipitations of hard TiC precipitates. [ABSTRACT FROM AUTHOR]

It has been proven that trace boron additions ( ≤ 0·4 wt-%) to titanium alloys can refine the as-cast microstructure significantly and improve the alloys' mechanical performance. This paper studied the structure of Ti6Al4V-0·1B ingot (Φ 300 mm) produced by vacuum arc remelting (VAR). It has been observed that the structure of Ti6Al4V-0·1B ingot in this experiment is not similar as that of earlier papers. The grain size in the centre of the ingot is 10 times larger than that of grains on the edge. This is because of the cooling speed of ingot as the edge cools faster than the centre in the process of VAR. Furthermore, this paper analysed the transverse and longitudinal tensile properties of Ti6Al4V-0·1B bar (Φ 100 mm) produced by free forging, which found that the transverse tensile elongation is only half of the longitudinal. Lots of TiB rods in transverse fracture were found, but not in longitudinal fracture. Microstructures of transverse and longitudinal bars were observed as well, which found TiB rods distributed along the axial, resulting in deterioration of the transverse tensile ductility. [ABSTRACT FROM AUTHOR]

Niobium and niobium alloys are normally produced by vacuum arc remelting (VAR) process. In the present work, the effect of various process parameters such as arc voltage, arc current (melt rate) and fill ratio on arc stability during VAR process and solidification structure of remelted niobium ingot is investigated. The effect of thermomechanical processing of VAR ingot on microstructure and mechanical properties is also investigated. It has been established that arc voltage is a function of arc length. For melting of niobium in 110 and 150 mm diameter crucibles, the optimum arc voltage is in the range of 34–37 V. It has been observed that the arc voltage needed for melting niobium is much higher than that used for melting stainless steels, reactive metals and superalloys. It has also been observed that for a given arc voltage, fill ratio has no significant influence on the melt rate of consumable electrode. However, arc current has significant influence on the melt rate and consequently on the solidification structure of the ingot. Thermomechanical processing of the VAR ingot is shown to result in significant increase in room temperature strength and ductility. However, the processing temperatures do not have any significant influence on the tensile properties. [ABSTRACT FROM AUTHOR]

High-speed camera imaging and optical emission spectroscopy have been used for investigating the structure of the electric arc and the transfer mechanisms of the liquid metal during vacuum arc remelting (VAR) of Ti alloys. The arc exhibited a similar operating regime to that described in the previous literature for the case of Inconel 718 and zirconium alloy electrodes. The arc behaved in a diffuse mode with many separate and rapidly moving cathode spots. Several parameters of the cathode spots, including their current, size and apparent velocity were evaluated. The application of an external axial magnetic field tended to encourage the cathode spots to locate themselves on the base of the electrode. A large density ratio of Ti+ ions and Ti atoms in the interelectrode plasma was evaluated, suggesting that the plasma was strongly ionized. The calculated excitation temperature of Ti+ ions (1-1.2 eV) was about 1.5-2 times greater than that obtained for Ti atoms. The transfer mechanisms of the drops of liquid metal might be classified into three main modes depending on the gap length: drop falling, drip short and drop erosion induced by the cathode spots. The importance of the influence of the arc on the metal transfer mechanisms was inversely related to the gap length. [ABSTRACT FROM AUTHOR]

The numerical simulation of remelting processes enables us to link the local solidification conditions to the operating parameters. Here, we discuss some recent studies aiming to develop specific aspects, e.g. the alternating current distribution during ESR of steels and superalloys, the ensemble arc motion in a VAR furnace and the influence of electromagnetic stirring on the macrosegregation in remelted ingots. [ABSTRACT FROM AUTHOR]

Abstract: This paper describes measurements of the voltage and temperature profiles in a vacuum arc remelting (VAR) crucible during a series of melts of a 40CrMoV13-9 steel alloy electrode, which were used to obtain information about the current flows in the furnace. The results derived included the current leaving the crucible above the ingot crown, the current flowing between the crucible and the crown, the current transferred between the crucible and the ingot lateral surface and the current flowing through the ingot bottom. It was established that the crown (observed to be 5–10cm high) played a predominant role in the current distribution, as the crown carried more than 50% of the furnace current. A small but non negligible fraction of the furnace current (about 10%), which represents the lower limit of the side-arcing current, was found to leave the crucible above the crown. The effect of the arc gap length on the current distribution was examined, but no general trend was clearly identified. Finally, a summary of the results reported in this study and those previously obtained in the literature is presented. Significant differences regarding the estimated amount of the side arcing current were noted that did not seem to be directly related to the changes in the remelted materials or melting conditions. It was pointed out that a detailed understanding of the current partition in the furnace requires additional experimental and theoretical study to clarify the path of the current flowing through the ingot crown. [Copyright &y& Elsevier]

method for identifying the sources of gas-containing metallurgical defects during the industrial smelting of Ti-6Al-4V titanium alloy using vacuum arc remelting technology was developed. The defect database that was obtained during long-term monitoring of an industrial process and the diffusion mechanism of the modification of defect sources in smelting underlie the development of this method. The results of metallographic studies and measurements of the microhardness and the oxygen, nitrogen, and aluminum concentrations in defects were used for identification. The concentrations of light element atoms in defects were measured by the nuclear microanalysis. This method allowed identification at an 80.0% level of efficiency. [ABSTRACT FROM AUTHOR]

The final solidification structures of Vacuum Arc Remelting (VAR) ingots depend on the temperature distribution and fluid motion within the molten pool. In this paper, a three-dimensional multi-physics macroscale model for VAR is developed, based on the modular CFD software PHYSICA. This model is used to provide estimates of process parameters and to study complex physical phenomena, such as liquid metal flow with turbulence, heat transfer, solidification, and magnetohydrodynamics in the VAR process. The macromodel is coupled to a microscale solidification model. The micromodel combines stochastic nucleation and a modified decentred square/octahedron method to describe dendritic growth with a finite difference computation of solute diffusion. The resulting multiscale model allows prediction of the formation of microstructures in the solidifying mushy zone. This gives a better understanding of the whole VAR process from operational conditions to final ingot microstructures, as well as an essential first step in defect prediction. [ABSTRACT FROM AUTHOR]

In order to produce Ni base superalloys for a critical use, it is necessary to control the whole processing route, and especially to master the solidification process. Thus, an essential step is the consumable electrode remelting operation (electroslag remelting or vacuum arc remelting) which produces the solidified ingot. Both processes are characterised by a fair control of the melting rate and a high cooling rate, even for large diameter ingots. Studies based on mathematical modelling and numerical simulation enable one to link the Iocal solidification conditions to the operating parameters. The present paper discusses the use and validation of numerical models for secondary melting. It is shown that modelling is a valuable tool for superalloy producers to prevent features such as white spot formation and to predict freckarling tendency. [ABSTRACT FROM AUTHOR]

Segregation defects greatly affect the service performance and working life of castings during the vacuum arc remelting (VAR) process. However, the corresponding research on the prediction of segregation defects is still not comprehensive. Through considering the influence of water-cooled crucible on the electromagnetic field inside an ingot, a full-scale model for the comprehensive prediction of freckles and macrosegregation defects during the VAR process is developed in this paper. The macroscopic solute transport phenomenon and the segregation behavior of Ni-5.8 wt% Al-15.2 wt% Ta alloy are predicted. The results indicate that the freckles are mainly concentrated in the lower region of the ingot. With the growth of the ingot, the solute enrichment channels gradually develop into solute enrichment regions, and the channel segregation evolves into macrosegregation. The Lorentz force mainly affects the flow pattern at the top of the molten pool, while the complex flow of multiple vortices is dominated by thermosolutal buoyancy. The maximum and minimum relative segregation ratio inside the ingot can reach 290% and −90%, respectively, and the positive segregation region accounts for about 79% of the total volume. This paper provides a new perspective for understanding the segregation behavior inside the ingot by studying the segregation evolution during the VAR process. [ABSTRACT FROM AUTHOR]

This study investigated the thermodynamic parameters, microstructures and electrochemical properties of TiMoVWCr and TiMoVNbZr bio-refractory high-entropy alloys (bio-RHEAs) prepared using the vacuum arc remelting process. The alloys were characterized using field emission scanning electron microscopy, field emission electron probe microanalyzer, X-ray diffraction analysis, and potentiodynamic polarization tests. The determined thermodynamic values of Ω-parameter, atomic size difference and valence electron concentration for the TiMoVWCr and TiMoVNbZr bio-RHEAs were within the range of solid solution formation. A high-temperature stable single BCC1 phase was obtained using the thermodynamic equilibrium calculations for the TiMoVWCr and TiMoVNbZr systems. The TiMoVWCr alloy microstructure comprised a dendrite, an inter-dendrite, and a second phase, while TiMoVNbZr alloy comprised a dendrite and an inter-dendrite. The TiMoVWCr alloy forming the stable single body-centered cubic solid solution demonstrated homogeneous microstructure and high phase stability. Moreover, pitting resistances of TiMoVWCr and TiMoVNbZr bio-RHEAs were remarkably superior to that of ASTM F75 alloy. • The TiMoVWCr alloy forming the stable single body-centered cubic solid solution demonstrated homogeneous microstructure and high phase stability. • Pitting resistances of TiMoVWCr and TiMoVNbZr bio-RHEAs were remarkably superior to that of ASTM F75 alloy. [ABSTRACT FROM AUTHOR]

The determination of an appropriate amount of turning for superalloy ingot surfaces, in a scientific and reasonable manner, is vital to the improvement of the metallurgical quality and comprehensive performance of superalloy ingots. In the present study, scanning electron microscopy with energy-dispersive spectroscopy, a high-temperature testing machine, a Brinell hardness tester and the Image-Pro Plus software were used to analyze and compare the types and amounts of inclusions, the average area of the (Al,Mg)O inclusions, and the mechanical properties of points at different distances from the edge of the GH4169 superalloy vacuum arc remelting (VAR) ingot edge. The effects of the amount of turning to which the superalloy is subjected, the metallurgical qualities, and the mechanical properties were systematically studied. The results showed that the five inclusion types did not change as the sampling locations moved away from the ingot edge, but the amount of inclusions and the average area of the (Al,Mg)O inclusions first decreased and then stabilized. Similarly, the tensile strength, elongation, section shrinkage, hardness, and fatigue life first increased and then stabilized. Finally, this experiment tentatively determined that an appropriate amount of turning for a GH4169 superalloy ingot is 36–48 mm. [ABSTRACT FROM AUTHOR]